Fibrous rod manufacturing is carried out by means of automatic methods, such as those shown in U.S. Pat. No. 3,455,766. Such rods are used extensively in cigarette filter making and are formed of continuous cellulose acetate tow which is first treated with plasticizer and then flooded with steam to accelerate the action of the plasticizer.
In the prior art at least one method, such as that shown in the above-mentioned U.S. Pat. No. 3,455,766, utilizes an endless, flexible, porous belt which is continuously moved through a treating and forming apparatus in processing machinery. The belt is wrapped around the material after the plasticizer is added to form the same into an elongated element. While the material is so confined in the belt, steam and then a cooling gas are passed through the belt and into contact with the tow material. This acts to first activate the plasticizer, a bonding constituent, in the material and then rigidify the tow material into a rod. After separation from the belt, the rod may be subdivided to form cigarette filter plugs or the like.
In the formation of the rod, an undesirable ridge is formed where the edges of the garniture belt meet in generally imperfect register to imperfectly complete the rod forming closure about the tow. A ridge remover is provided for smoothing the undesirable ridge, such as that shown in said U.S. Pat. No. 3,455,766. However, such a prior ridge remover as is shown and described in said U.S. Pat. No. 3,455,766 and other designs have not fully met the need for producing a smooth radius at the ridge location. Cigarettes made with filters having a ridged surface of this type may pass unfiltered smoke adjacent the ridge line thereby bypassing the filter and at least partially negating the basic function of the filter. It is highly desirable to, therefore, produce a filter with a substantially uniformly smooth surface comprising a relatively uniform radius of curvature about the whole periphery.